3270 controller simulation

Grant Taylor cctalk at gtaylor.tnetconsulting.net
Mon Nov 18 11:52:48 CST 2019

On 11/18/19 10:38 AM, Dave Wade wrote:
> I go TN3270 from the 3174 -> Hercules so the screens look like local 
> screens to the OS. This is how most folks have done it.

I forgot about the fact that Hercules, not the mainframe OS, is doing 
some translation.

Do you know what protocol name would be used to describe the 
communications between the mainframe OS and what it thinks are locally 
attached terminals?

> It needs a big(ish) 3174 and the C6.3 or 6.4 microcode.


> As MVS 3.8J does not understand DLSw (it has no TCP) Matt unpicks the 
> DLSw in Hercules so MVS sees (I think) an SDLC connected 3174.

Hum.  ...  Very intriguing.

Am I understanding you correctly to mean that Hercules itself has some 
DLSw functionality?

Part of me wants to ask if the 3174 support can be used for SNA out of 
the mainframe, as in the below diagram.  But my reading of various 
pieces of Hercules documentation indicate that it can't be done (yet).

[Mainframe OS]---(SDLC)---[Hercules 

> You are not being obtuse. IBM networking covers so many options its 
> not true.

Thank you for understanding.

> I think TN3270 connected screens usually look like they are "local"....


> Define "most" and "when".

"most", in this context, is more to allow for my loose understanding and 
zero exposure.

I'm not tracking "when".

> I have 4 x 3174s plus the guts of two more. None have channel interfaces.

Do you have the model numbers handy?  (I assume the all the type numbers 
are 3174.)

> The first three I bought years ago had token ring interfaces and serial 
> interfaces which I think can be bi-sync or SDLC.
> Two of the others have token ring, and one has ethernet. I think many 
> connected over token ring...

That sounds like Remote 3174s.  At least based on my limited and likely 
flawed understanding.

My understanding is that:

  · Local 3174s were channel (?) attached to the host.
  · Remote 3174s were SDLC / X.25 / Token Ring / Ethernet connected to 
Local 3174s.

Where "local" is physically close to and connected to the host. 
Similarly "remote" is not physically close nor connected to the host.

Grant. . . .
unix || die

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